1. Field of the Invention
The present invention relates to apparatus and method for purifying polluted water, and more particularly to apparatus and method for performing an aerobic treatment on polluted water and at the same time separating and capturing suspended fine solid materials (pollutants) from the polluted water to perform an anaerobic treatment on the polluted water.
2. Description of Related Art
Various methods have been hitherto proposed and practically used as a method of purifying various kinds of polluted water, such as waste water or river water which is polluted by waste water. The conventional polluted water purifying methods are mainly classified into (1) a physical/chemical treatment method and (2) a biological treatment method. As the physical/chemical treatment method are known a method for separating and removing suspended materials, etc. from polluted water by means of precipitation, filtering or the like, a method for chemically treating pollutants with chemicals to make the pollutants harmless; and a method of separating and removing pollutants from polluted water by means of agglomeration or precipitation. Further, as the biological treatment method are known a method of aerobically treating polluted water with a biomembrane or an active sludge to flocculate pollutants and separate and remove the pollutants from polluted water; and a method of anaerobically treating polluted water to digest (liquefy) the pollutants.
The biological treatment method utilizes a decomposition action of microorganism in natural field, so that its reaction is moderate. In addition, its process needs no chemical, and thus it does not bring various troubles due to the chemicals. Therefore, the biological treatment method has been favorably used, and various developments for this method are vigorously being made.
With respect to the method using the active sludge, various systems which are concentrically based on two processes of an aeration process and a sedimentation process have been proposed and practically used. With respect to the method of forming a biological film on a carrier, various kinds of carriers are proposed. For example, Japanese Laid-open Patent Application No. Sho-63-310696 proposes a hollow spherical carrier which forms an aerobic state and an anaerobic state at the same time. Further, there is also proposed an aerobic/anaerobic treatment which forms aerobic and anaerobic states by means of a hollow cylinder having a honeycomb construction of a high surface area.
However, in all the conventional biological treatments as described above, a long process time of at least 5 to 11 hours is generally required over all the steps of a purifying treatment. For example, in the method using the active sludge and the aerobic treatment method using the biomembrane formed on the surface of the carrier, a sedimenting pool is provided at a front stage to perform a predetermined sedimenting treatment on polluted water, and then the polluted water is finally treated while held up in an aerobic purification area for a retention time of several hours or more, whereby a predetermined environmental quality standard value is satisfied. In the active sludge method, there is a manner of performing the aeration treatment for about two hours; however, it has a disadvantage that a BOD removal rate may be reduced. Further, in the aerobic/anaerobic purifying treatment method using the hollow carrier, the diameter of holes through which the inside and the outside of the hollow carrier are communicated to each other is set to 0.05 to 1 mm, and thus the flow-in and flow-out of the polluted water into and from the inside of the hollow carrier is not smoothly performed, so that it needs a longer time than the anaerobic treatment in the inner space of the hollow carrier and this is not efficient.
Recently, a so-called inter-conglomerate contact oxidation method which purifies polluted river water by using river beds has been proposed and practically used as one of the biological treatments for polluted water. In the inter-conglomerate contact oxidation method, a conglomerate layer is formed by effectively using conglomerate, such as gravel in the river, or the like, and river water is made to flow (passed) through the conglomerate layer for a biological treatment, whereby BOD (Biochemical Oxygen Demand) and SS (Suspended Solid) can be greatly reduced. Therefore, much attention is paid to this method as a purification method for polluted water, such as polluted river water, or the like.
The inventor of this application has vigorously studied a treatment method in which the purification technique using the inter-conglomerate contact oxidation method can be practically used for a general water treatment device (not to a large-scale facility using a huge river bed, for example) and polluted water can be efficiently purified. As a result of the vigorous studies, the inventor developed a separation member forming a purification treatment system which is completely different from the conventional treatment for polluted water, and previously proposed the separation member and a polluted water treatment using the separation member in Japanese Laid-open Patent Application No. Hei-3-221110. Further, in Japanese Laid-open Patent Application No. Hei-6-343990, which corresponds to U.S. Pat. No. 5,565,103, the inventor proposed a suitable flow-separating method and a flow-separating member in consideration of such a flow-separating phenomenon that suspended fine solid materials are separated and removed from polluted water as flowing fluid with effectively using fluid energy on the basis of the behavior of the suspended fine solid materials.
In the flow-separating member and the flow-separating method as described above, the polluted water is subjected to an aerobic treatment on the surface. The suspended solids (SS) can be efficiently captured by the flow-separating member for a relatively short time to separate and remove the SS from the polluted water, and captured organic SS can be anaerobically treated in voids of the flow-separating member to make the organic SS liquid and soluble. Therefore, this method can simply perform the purification treatment for polluted water in one step for a short time, and thus it is expected to be an extremely excellent treatment method for polluted water.
This method has been achieved mainly to remove SS, and it has been also proved for this method that the aerobic treatment on the surface of the flow-separating member is enhanced and thus the BOD removal rate is effectively enhanced because the surface area of the flow-separating member is increased more than the inter-conglomerate contact oxidation method. However, it would not effectively work from the viewpoint that it must be applicable to any polluted water and it must meet any requirement. Particularly, if it is required to perform a purification treatment on polluted water containing a large amount of BOD at a desired BOD removal rate for a short time, this method does not sufficiently satisfy this requirement.